<h1>Missing Heartbeat Detection</h1>
Services on the device may log a kind of "Heartbeat" message into syslog. The idea is to be able to detect whenever such a message
no longer appear on the server. It is important to understand that we're not trying to detect if a service fails, because a service
is usually capable of logging error messages itself. However, we want to detect if a service is simply dead, an no messages 
appear at all! 
<h2>An example</h2>
<b>Find the expression</b><br>
One example could be to monitor the occurrence of "SIP registrations". Simply find an expression
which covers both the "SIP registration OK" and "SIP registration ERROR", since both of these cases reflect a working/active 
service on the client. Once you have the correct expression (use Syslog Search to test it out), you specify this in the
expression field.<p> 
<b>Decide on group</b><br>
Make sure to specify a group which covers the set of Units where the service is supposed to run. The Group could perhaps
be all the devices which have the SIP-"Enabled"-parameter set to "1".<p> 
<b>Timeout</b><br>
Specify a number of hours as timeout. If no message matching the expression if found within the last timeout-hours, then
the Heartbeat is deemed missing.
<h2>Result</h2>
The result of this is that the server will generate a HEARTBEAT-MISSING message for every Unit where the Heartbeat has stopped. 
All the messages will contain "HEARTBEAT-MISSING" and the expression used. The system will insert this message every hour 
for as long as the service is dead.
<h2>What to do with it?</h2>
Now that the system produces messages of this kind, you can setup a Syslog Event to trap this Missing Heartbeat! Furthermore, a
Syslog Event can be used in a Trigger, to generate an alarm. In effect, you can then get alarm, if some or many devices
loose their services.
